In the manufacturing of semiconductor devices, trace amounts of oxygen has a detrimental effect. In the etching of an aluminum film, oxygen promotes the formation of Al.sub.2 O.sub.3, which becomes a barrier to the etching of ALUMINUM (Al) films. In the etching of oxide over silicon, with a typical CHF.sub.3 /CF.sub.4, the presence of oxygen shifts the F/C ratio in the favor of the F, by reacting with the Carbon. The excess F then increases the etch rate of the silicon, thereby decreasing the selectivity of the etch.
This problem is typically handled by a chemical process, for example, in the etching of Al, one of the process gases is BCl.sub.3. The principal function of this gas is to react with the Al.sub.2 O.sub.3 formed on the Al surface and to getter any oxygen in the reactor via the formation of B.sub.2 O.sub.3. With this procedure, chemical side-effects are created. B.sub.2 O.sub.3 is deposited through the vacuum system, which a serious problem from the viewpoint of particles and general rector cleanliness.